The present invention relates to a method for directly obtaining a sample of the serum or continuous liquid phase, or a mixture of the continuous phase and a portion of the discontinuous phase of a dispersion of a discontinuous phase within a continuous liquid phase. More particularly the present invention relates to a relatively rapid sampling method for analysis of the continuous phase or a mixture of continuous and discontinuous phases of a liquid emulsion or dispersion.
Liquid emulsions and dispersions may be natural or synthetic. Naturally occurring emulsions and dispersions include such diverse products as milk and natural rubber latex. Synthetic emulsions and dispersions include monomeric emulsions and dispersions of polymers in a continuous liquid phase such as latex. In the production of emulsions and dispersions of polymers an analysis of the continuous phase provides a method for monitoring both the instantaneous and overall conversion to better control the process and to control polymer properties. In a finished latex the analysis of the continuous phase or select segments of the discontinuous phase provides insight into the chemicals and methods used in the polymerization.
There have been a number of proposals for the analysis of latex. Mechanically the serum may be separated from the polymer by centrifuging. Chemically the polymer particles may be absorbed onto the surface of various types of columns such as in isotachophoresis (Chemical Abstracts 104:51408n).
U.S. Pat. No. 4,529,521 issued July 16, 1985, assigned to The Dow Chemical Company discloses a hollow-fibre method for dialyzing a serum from a sample of latex then subjecting the dialyzate (the material passing through the membrane) to high pressure liquid chromatography to determine residual monomers or unincorporated oligomers in the aqueous phase. While the process is useful it has one drawback. It permits a sampling of the serum with solutes having a molecular weight up to about 9000. It does not allow one to-pick out a selected segment of the higher polymeric portion of the dispersion.
In the hollow fiber dialysis process the fibers must be clean. This means either disposing of the fibers after each analysis or flushing and cleaning the fibers. The latter is a time consuming step. While the cost of hollow fibers for the dialysis method may seem trivial., one of the areas where rapid serum and/or latex analysis is required is in monitoring the progress of a polymerization. The cost of a fiber bundle for dialysis is in the order of $50.00 whereas the cost of the filters and a disposable syringe useful in the present invention is in the order of $3.00 to $5.00. If you wish to conduct, for example, three analysis over a 6 to 8 hour polymerization, the dialsyis process would add a cost of $150.00 to the resulting product whereas the present method would permit a comparable analysis at a cost of about $10.00 to $15.00.
The separation of various particle sizes of polymer according to the present invention gives a suggestion of the methods used to make the dispersion. This is helpful from the point of view of "reverse" engineering a latex. The same techniques are extremely useful in following the progress of a polymerization and controlling the process and the polymer properties. The present invention is directed to the analysis of dispersions or emulsion. It is known to separate bulk admixtures such as oil in water, by filtration using a No. 41 or 42 filter paper.